[PATCH] drm/ttm: fix ttm tt init fail when size exceeds kmalloc limit

[Christian König]

Am 20.04.22 um 11:07 schrieb Wang, Yang(Kevin):
>
> [AMD Official Use Only]
>
>
>
> ------------------------------------------------------------------------
> *From:* Koenig, Christian <Christian.Koenig at amd.com>
> *Sent:* Wednesday, April 20, 2022 5:00 PM
> *To:* Wang, Yang(Kevin) <KevinYang.Wang at amd.com>; 
> dri-devel at lists.freedesktop.org <dri-devel at lists.freedesktop.org>; 
> amd-gfx at lists.freedesktop.org <amd-gfx at lists.freedesktop.org>
> *Subject:* Re: [PATCH] drm/ttm: fix ttm tt init fail when size exceeds 
> kmalloc limit
> Am 20.04.22 um 10:56 schrieb Yang Wang:
> > if the __GFP_ZERO is set, the kvmalloc() can't fallback to use vmalloc()
>
> Hui what? Why should kvmalloc() not be able to fallback to vmalloc()
> when __GFP_ZERO is set?
>
> And even that is really the case then that sounds like a bug in 
> kvmalloc().
>
> Regards,
> Christian.
>
> [kevin]:
> it is really test case from libdrm amdgpu test, which try to allocate 
> a big BO which will cause ttm tt init fail.


LOL! Guys, this test case is intended to fail!

The test consists of allocating a buffer so ridiculous large that it 
should never succeed and be rejected by the kernel driver.

This patch here is a really clear NAK.

Regards,
Christian.

> it may be a kvmalloc() bug, and this patch can as a workaround 
> in ttm before this issue fix.
>
> void *kvmalloc_node(size_t size, gfp_t flags, int node)
> {
> ...
>       if ((flags & GFP_KERNEL) != GFP_KERNEL)
>               return kmalloc_node(size, flags, node);
> ...
> }
>
> Best Regards,
> Kevin
>
> > to allocate memory, when request size is exceeds kmalloc limit, it will
> > cause allocate memory fail.
> >
> > e.g: when ttm want to create a BO with 1TB size, it maybe fail.
> >
> > Signed-off-by: Yang Wang <KevinYang.Wang at amd.com>
> > ---
> >   drivers/gpu/drm/ttm/ttm_tt.c | 14 +++++++++++---
> >   1 file changed, 11 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
> > index 79c870a3bef8..9f2f3e576b8d 100644
> > --- a/drivers/gpu/drm/ttm/ttm_tt.c
> > +++ b/drivers/gpu/drm/ttm/ttm_tt.c
> > @@ -97,9 +97,12 @@ int ttm_tt_create(struct ttm_buffer_object *bo, 
> bool zero_alloc)
> >   static int ttm_tt_alloc_page_directory(struct ttm_tt *ttm)
> >   {
> >        ttm->pages = kvmalloc_array(ttm->num_pages, sizeof(void*),
> > -                     GFP_KERNEL | __GFP_ZERO);
> > +                                 GFP_KERNEL);
> >        if (!ttm->pages)
> >                return -ENOMEM;
> > +
> > +     memset(ttm->pages, 0, ttm->num_pages * sizeof(void *));
> > +
> >        return 0;
> >   }
> >
> > @@ -108,10 +111,12 @@ static int 
> ttm_dma_tt_alloc_page_directory(struct ttm_tt *ttm)
> >        ttm->pages = kvmalloc_array(ttm->num_pages,
> > sizeof(*ttm->pages) +
> > sizeof(*ttm->dma_address),
> > -                                 GFP_KERNEL | __GFP_ZERO);
> > +                                 GFP_KERNEL);
> >        if (!ttm->pages)
> >                return -ENOMEM;
> >
> > +     memset(ttm->pages, 0, ttm->num_pages * (sizeof(*ttm->pages) + 
> sizeof(*ttm->dma_address)));
> > +
> >        ttm->dma_address = (void *)(ttm->pages + ttm->num_pages);
> >        return 0;
> >   }
> > @@ -120,9 +125,12 @@ static int 
> ttm_sg_tt_alloc_page_directory(struct ttm_tt *ttm)
> >   {
> >        ttm->dma_address = kvmalloc_array(ttm->num_pages,
> > sizeof(*ttm->dma_address),
> > -                                       GFP_KERNEL | __GFP_ZERO);
> > + GFP_KERNEL);
> >        if (!ttm->dma_address)
> >                return -ENOMEM;
> > +
> > +     memset(ttm->dma_address, 0, ttm->num_pages * 
> sizeof(*ttm->dma_address));
> > +
> >        return 0;
> >   }
> >
>
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